Conventionally, zoom lenses of the two group or the three group type having leading negative lens groups (a configuration in which negative lens groups are provided toward the object side) are well known as zoom lenses to be provided in compact digital cameras, compact video cameras, and portable terminal devices. For example, Japanese Unexamined Patent Publication No. 2010-091948 discloses examples of a two group type zoom lens and a three group type zoom lens. As disclosed in Japanese Unexamined Patent Publication No. 2010-091948, aberrations can be corrected more advantageously by providing lenses toward the image side of the second lens group to adopt a three group configuration. In addition, this configuration increases the degree of freedom in design. Therefore, the advantageous effects of improved performance, miniaturization, and increased variable magnification ratio can be obtained.
Here, use of lower cost plastic lenses may be considered as a measure to reduce the cost of zoom lenses. There are many zoom lenses of the two group type and the three group type, which are employed in compact digital cameras and the like, that have a configuration in which the first lens group is constituted by a negative lens and a positive lens provided in this order from the object side. Between these two lenses, the positive lens is easier to form using a plastic material, from the viewpoint of molding properties.
Forming a positive lens of a first lens group using a plastic material has also been proposed (refer to Japanese Unexamined Patent Publication No. 2007-025373 and Japanese Unexamined Patent Publication No. 2007-187740, for example). More specifically, Japanese Unexamined Patent Publication No. 2007-025373 discloses that a positive lens of a first lens group is formed by a material having a refractive index of 1.58 and an Abbe's number of 30.9. In addition, Japanese Unexamined Patent Publication No. 2007-187740 discloses that a positive lens of a first lens group is formed by a material having a refractive index of 1.61 and an Abbe's number of 26.6. It is preferable for the difference between the Abbe's numbers of the positive lens of the first lens group and a negative lens of the first lens group to be great. Therefore, it is desirable for a material having a smaller Abbe's number to be employed for the positive lens.
Japanese Unexamined Patent Publication No. 2006-039182 and U.S. Patent Application Publication No. 20070171544 disclose that a material having an Abbe's number within a range from 23 to 24 is employed as the material of a positive lens, in order to increase the difference between the Abbe's numbers of the positive lens and a negative lens of the first lens group